326 NEW YORK STATE MUSEUM 



the Hamilton shales, and, if the locality record is correct, it is probably 

 from the Ithaca fauna of Chenango county and may be a fragment of our 

 species, Carinaropsis ithagenia. 



Diagnosis. Shell of medium size. In early growth the whorls are 

 involute, narrow, regularly convex and umbilicate ; inner lip always slightly 

 calloused ; at mature growth the last whorl is abruptly and greatly 

 expanded, the margin of the aperture generally assuming a transversely 

 subcordate outline, the sides approaching anteriorly and the greatest diam- 

 eter of the peristome being back of the middle. The lip is reflected back- 

 ward over the calloused penultimate whorl or may be transected by it. It 

 is this reflection of the inner peristome that closes the umbilicus on the last 

 volution. The callus in the adult condition is developed into a transversely 

 septiform projection, entering the interior cavity. This takes the form of a 

 plate thickened axially both on the upper and under sides and excavated or 

 thin at the sides. The median thickening is pinched together and narrowed 

 and projects farthest. The entire structure when the shell is compressed in 

 the shale gives the impression of a platform similar to that in Carinaropsis. 

 but it is of quite different character. The slit band is narrow with elevated 

 margins ; it makes a deep emargination on the outer lip and is clearly 

 defined over the entire final volution, but is seldom visible on young shells. 

 Surface smooth or with only fine lines and festoons concentric to the 

 margin. 



Dimensions. In an average specimen the aperture has a vertical diam- 

 eter (width) of 18 mm and a horizontal diameter (hight) of 23 mm. 



Habitat. Genesee province ; Naples subprovince. Very common in 

 the soft shales of the lower part of the group at and about Naples and at 

 localities in Livingston county ; also on Cashaqua creek. In the eastern 

 region at Bennettsburg and Beaver Dams, Schuyler co. In the Styliola 

 limestone, Canandaigua lake. 



